Band-reject Filter Research Articles

Tunable narrow band-rejection and band-pass filter based on long-period waveguide grating on a thin-film lithium niobate rib waveguide

We propose and demonstrate experimentally an electro-optic (EO) and thermo-optic (TO) tunable wavelength filter with band-rejection and band-pass dual-function. Our proposed filter is based on a long-period waveguide grating (LPWG) formed on a lithium niobate on insulator (LNOI) rib waveguide with a channel-shaped polymer cladding waveguide. The LPWG formed on the surface of the LNOI core enables efficient mode coupling between the two fundamental modes of the LNOI waveguide and the polymer cladding waveguide and hence dual-function filtering. For the z-/x-polarized input light, our fabricated best filter shows an 18.1-dB/8.2-dB band-rejection contrast and a 15.7-dB/17.4-dB band-pass contrast at 1565.26/1594.24 nm wavelength, with a relatively narrow 3-dB bandwidth of 2.5/2.3 nm, respectively. In addition, the fabricated filter also shows an EO tuning efficiency of ∼32 pm/V and a TO tuning efficiency of 0.465 nm/°C, respectively. Our proposed filter could find applications in wavelength division multiplexing, temperature sensing, and other fields of optical communication and optical information processing.

Hanning FIR window filtering analysis for EEG signals

The window function is a mathematical function in signal processing that is multiplied by a signal to lessen or eliminate the impact of undesired characteristics such as spectral leakage and edge effects that might arise while analyzing finite-duration signals. The Hanning window is just one of several window functionalities available. It is designed to gradually taper the endpoints of a signal to zero, reducing spectral leakage in the frequency domain. Filtering is commonly employed in Electroencephalography (EEG) signal processing to remove noise, artifacts, or undesired frequency components while retaining the desired information. Filtering techniques include band pass, low pass, and high pass and band reject filtering. Hanning window technique using low pass, high pass, band pass, and band reject is used for filtering of EEG signal. The response time analysis for the Hanning window is calculated using low, high, band pass, and band-reject filters for different types of EEG waves alpha, beta gamma, theta, and delta using the signal processing simulation tool MATLAB 2023. The response time for delta wave using a low pass filter has a low response time of 14.125 sec which is comparatively less than another filter. For theta wave high pass filter has a low response time of 11.965 seconds. For alpha wave low pass filter has a low response time of 16.706 seconds whereas for beta wave low pass filter has a low response time of 15.202 seconds. For gamma waves high pass filter has a low response time of 11.349 seconds. Hanning band-reject filter has proven low response time for delta, theta, and gamma waveforms of 16.475 seconds, 16.182 seconds, and 17.743 seconds respectively. The novelty of the work is that the Hanning window improves frequency resolution by balancing the main lobe width with side lobe attenuation Hanning band-reject filter is suited best to figure out the widest main-lobe peak and highest peak for different EEG waveforms.

Frequency-Tunable SIW Band-Reject Filter with Increased Fundamental Mode Bandwidth for Spectrum Underlay Cognitive Radio

This paper presents the design of a frequency-tunable substrate-integrated waveguide (SIW) band-reject filter, specifically for spectrum underlay cognitive radio operation. The proposed filter has a simple tuning circuit but provides a wide frequency tuning range from 2.9 to 4.4 GHz (41%). The second resonant mode has been suppressed using a simple quadrature coupling; hence, the fundamental mode bandwidth of the filter has been increased from 2.08 GHz to 3.36 GHz. Due to its wide tuning range, simple tuning circuit, and increased fundamental mode bandwidth, the proposed filter is greatly important in underlay cognitive radio construction. The second-order filter has also been developed, and its performance is analyzed with both simulation and measurement. It gives a tunable bandwidth of 41%, an insertion loss of more than 10 dB, and a fundamental mode bandwidth of 3.36 GHz. The filter performance is also analyzed after connecting it to the standard horn antenna. Finally, from the total efficiency plots, it has been concluded that the proposed filter achieves all the above advantages with a low-lossy nature.

A Dual-Band Polarization-Insensitive Frequency Selective Surface for Electromagnetic Shielding Applications.

This paper presents a novel polarization-insensitive dual-band frequency-selective surface (FSS)-based electromagnetic shield. The miniaturized FSS unit cell consists of a modified Jerusalem crossed loop and a corner-modified square loop. These FSS elements are arranged in a co-planner configuration over a single-layer Rogers 5880 substrate and simultaneously offer effective shielding in the X- and Ku-bands. Moreover, the FSS manifests polarization-independent and angularly stable band-reject filter characteristics over various oblique angles of incidence for both the TE and TM polarizations with virtuous attenuation at both resonances. In addition, the FSS structure is modelled into an equivalent lumped circuit to better analyze the phenomenon of EM wave suppression. A finite prototype of FSS is fabricated and tested. The simulated and measured results are in good agreement, thus making it a potential candidate for RF shielding/isolation applications.

Antenna Booster Element for Multiband Operation.

The escalating demand for versatile wireless devices has fostered the need to reduce the antenna footprint to support the integration of multiple new functionalities. This poses a significant challenge for the Internet of things (IoT) antenna designers tasked with creating antennas capable of supporting multiband operation within physical constraints. This work aims to address this challenge by focusing on the optimization of an antenna booster element to achieve multiband performance, accomplished through the design of a band-reject filter. This proposal entails a printed circuit board (PCB) measuring 142 mm × 60 mm, with a clearance area of 12 mm × 40 mm, incorporating an antenna booster element of 30 mm × 3 mm × 1 mm (0.07 λ). This configuration covers frequencies in the LFR (low-frequency range) from 698 MHz to 960 MHz and the HFR (high-frequency range) from 1710 MHz to 2690 MHz. A theoretical analysis is conducted to optimize bandwidth in both frequency regions. Finally, a prototype validates the analytic results.

Dual-port circularly polarized dielectric resonator–based antenna with reconfigurable integrated multifunctional filter for 5G cognitive radio applications

Abstract In this paper, the design of a circularly polarized (CP) multiple-input–multiple-output (MIMO) antenna system is presented, utilizing a dielectric resonator (DR). This presented antenna system is subsequently integrated with a multifunctional filter, all meticulously structured on a single substrate. The multifunctional filter operates in three modes: reconfigurable band-pass and band-reject filter as well as all-pass filter. The overall structure works as a tunable filtenna. The designed filtenna is expanded into a two-port MIMO system on a unified substrate, providing strong port isolation below −28.5 dB. The overall dimension of proposed radiator is 180 × 180 × 1.6 mm3. The value of peak gain is 5.19 dBic. By switching the states of PIN diodes, the designed filtenna operates as a sensing and communicating antenna for interweave and underlay cognitive radios (CRs). The proposed antenna supports the CP waves within the working band, i.e., 3.6–4.5 GHz. The simulated results are validated by comparing them with the measured results showing less variation among them. MIMO parameters, including the envelope correlation coefficient and diversity gain, have been calculated for the proposed filtenna, representing its suitability for 5G-CR applications.

Mitigating SSO in an Actual DFIG-MTDC System: Field Implementation and Tests

Recently, a new type of subsynchronous oscillation (SSO) event was observed in the doubly fed induction generator (DFIG)-based wind farm connected to a multi-terminal dc (MTDC) grid. It has been established that converter-based devices can interact with each other and other grid components. Generally, it is difficult to replicate an SSO event and devise a mitigation scheme due to the complex and black-box nature of converter-based devices. This paper demonstrates the field implementation of a model-independent method to mitigate the SSO using additional band-rejection filters in the DFIG's converter controller. The proposed method is unique in the sense that the complete design and implementation were carried out without detailed models or prior EMT studies. Field results illustrate that the risk of SSO can be significantly reduced by supplementing the DFIGs with properly tuned band-rejection filters, which reshape the DFIGs' impedance characteristics at the desired frequency. The test results obtained under various operating conditions further confirm the effectiveness of the mitigation scheme. The implementation and field tests of the filter-based mitigation scheme in an actual system can provide a practical reference for solving similar SSO issues in other large-scale systems without going through detailed EMT studies.

Equatorial Ionospheric Scintillation Measurement in Advanced Land Observing Satellite (ALOS) Phased Array-Type L-Band Synthetic Aperture Radar (PALSAR) Observations

Amplitude stripes imposed by ionospheric scintillation have been frequently observed in many of the equatorial nighttime acquisitions of the Advanced Land Observing Satellite (ALOS) Phased Array-type L-band Synthetic Aperture Radar (PALSAR). This type of ionospheric artifact impedes PALSAR interferometric and polarimetric applications, and its formation cause, morphology, and negative influence have been deeply investigated. However, this artifact can provide an alternative opportunity in a positive way for probing and measuring ionosphere scintillation. In this paper, a methodology for measuring ionospheric scintillation parameters from PALSAR images with amplitude stripes is proposed. Firstly, sublook processing is beneficial for recovering the scattered stripes from a single-look complex image; the amplitude stripe pattern is extracted via band-rejection filtering in the frequency domain of the sublook image. Secondly, the amplitude spectrum density function (SDF) is estimated from the amplitude stripe pattern. Thirdly, a fitting scheme for measuring the scintillation strength and spectrum index is conducted between the estimated and theoretical long-wavelength SDFs. In addition, another key parameter, the scintillation index, can be directly measured from the amplitude stripe pattern or indirectly derived from the scintillation strength and spectrum index. The proposed methodology is fully demonstrated on two groups of PALSAR acquisitions in the presence of amplitude stripes. Self-validation is conducted by comparing the measured and derived scintillation index and by comparing the measurements of range lines and azimuth lines. Cross-validation is performed by comparing the PALSAR measurements with in situ Global Position System (GPS) measurements. The processing results demonstrate a powerful capability to robustly measure ionospheric scintillation parameters from space with high spatial resolution.

Mechanically Induced Long-Period Fiber Gratings and Applications

Long-period fiber gratings (LPFGs) functioning as band-reject filters have played a pivotal role in the realm of optical communication. Since their initial documentation in 1996, LPFGs have witnessed rapid advancements in areas such as optical sensing, the equalization of optical amplification, and optical band-pass filtering, etc. The unique attributes of optical fiber-based grating, including their miniaturized size, cost-effectiveness, and immunity to electromagnetic interference, have contributed significantly to various sectors over the last two decades. This paper presents a review of the evolution of LPFGs, with a specific focus on the progression and current trends of mechanically induced long-period fiber gratings. It offers a concise overview of coupled-mode theory, the fabrication processes, the merits, and the limitations associated with mechanically induced LPFGs. Moreover, this review elucidates the application methodologies of mechanically induced LPFGs and anticipates future directions in this field.

Spin dynamics of room temperature van der Waals (vdW) ferromagnets and their usage in microwave devices

Quasi-two-dimensional van der Waals (vdW) materials exhibiting room-temperature (RT) long-range ferromagnetic nature have emerged as a significant research field to explore fundamental condensed matter physics due to their intriguing physical properties. These vdW materials enable a futuristic platform for implementing novel spintronics devices. Here, we examined the spin dynamics of polycrystalline Fe5GeTe2 and Fe4.8Co0.2GeTe2 vdW materials using ferromagnetic resonance (FMR) spectroscopy. Vibrating Sample Magnetometer (VSM) study reveals that both materials have a soft ferromagnetic character at room temperature. From room temperature FMR measurements, the effective magnetization of Fe5GeTe2 and Fe4.8Co0.2GeTe2 derived ∼0.54 ± 0.056 and 0.50 ± 0.017 kOe, respectively. These results are consistent with reported VSM data. Fe5GeTe2 and Fe4.8Co0.2GeTe2 exhibit broad FMR linewidths of 0.697 ± 0.036 and 0.748 ± 0.056 kOe, respectively, which can be due to inhomogeneous line broadening. Besides its intrinsic contribution to linewidth, it is also affected by extrinsic Gilbert damping (αext). The value of αext is influenced by conflicting intra-band and inter-band electronic transitions, according to Modified Kambersky's theory. Furthermore, the effective Gilbert damping constant (α) obtained is 0.0513 ± 0.0046 for Fe5GeTe2 and 0.0526 ± 0.0031 for Fe4.8Co0.2GeTe2 at RT. Additionally, we developed microwave signal processing devices using these materials and evaluated their functionality both as a microwave band-reject filter and an adjustable phase shifter. The stop-band response was studied across the 5 to 25 GHz frequency range under an applied magnetic field as high as 7 kOe. For these flip-chip-based devices, attenuation is −5 dB/cm for the Fe5GeTe2-based filter and −3.2 dB/cm on sample Fe4.8Co0.2GeTe2 at 6.95 and 5.37 kOe, respectively. The same micro-strip filter was used as a tunable phase shifter in the off-resonance region. The optimal differential phase shift studied for Fe5GeTe2 and Fe4.8Co0.2GeTe2-based phase shifters in the high-frequency region (22 GHz for Fe5GeTe2 and 18 GHz for Fe4.8Co0.2GeTe2) is 23°/cm and 14°/cm, respectively, at high magnetic fields. These versatile devices find integration across a wide spectrum of applications, such as phased-array antennas, radar systems, and wireless communication systems, offering their benefits to diverse fields.

Synchronously tunable combined four-channel ferrite filter

The original design of the synchronously tunable combined four-channel ferrite filter is given. It is a functional unit consisting of four microwave systems of ferrite filters with coupling loops (one such microwave system in each channel) and a common magnetic system for these filters, which ensures their synchronous tuning in the frequency range of 2-4 GHz. The structural solution of the microwave system in the form of a module allows one to obtain both a bandpass ferrite filter and a band-reject ferrite filter. The results of experimental research are provided. They showed that such a four-channel controllable ferrite filter has not only improved design and technological indicators but also a high decoupling between channels. It can be successfully used not only in measuring equipment but also in modern multichannel microwave communication equipment and radar.

Description of the State primary standard for length, velocity, and acceleration units at the oscillating movement of solid body NDETU AUV-04-2019

The article describes the state of metrological assurance in Ukraine, the field of vibration measurements, the composition of the State primary standard for length, velocity, and acceleration at oscillating movement NDETU AUV-04-2019, and its general characteristics and functioning principles. And attention is paid to the key comparisons in which this standard had taken part. The ways of standard upgrading are considered.

Designing cladding mode interference device – a host for sensors and all-fiber inline gain-flattening component and broad-band filter

This article describes how to devise interference and self-imaging of core and cladding modes based devices using dissimilar core concatenated all-fibers. The core diameter mismatch in the structure excites the cladding modes with the core mode that leads to a progressive interference imaging between the cladding modes and the core mode yielding wavelength and refractive index dependent loss. Through a systematic study, we tune the device parameters to gauge temperature and concentration with sensitivity of 0.0713 dB/°C and 0.0372 dB/(% mL/mL) respectively as a high-performance fiber sensor. Next, optimizing the wavelength sensitive parameters of the host configuration, we investigate the transmission characteristics as gain-flattening filters (GFF) of Erbium-doped fiber amplifiers (EDFAs) with maximum gain variations of 0.91 and 0.97 dB, for two different EDFAs respectively over a wavelength band of 33 and 25 nm. Finally, we demonstrate a tunable and two-flattop band rejection filters with rejection band of 14, 26 and 46 nm, respectively.

The Versatile All-pass Filter

It is shown that two other types of filters, viz., band-pass and band-reject, can be derived from a given all-pass filter. For illustration, we consider RC active all-pass filters, and show how starting from such a given circuit, one can obain band-pass or band-reject filters, simply by subtraction from, or addition to, unity, to the all-pass one. The corresponding circuit diagrams for implementations are also shown, and simulation plots have been drawn to illustrate the validity of the above facts.

A novel and ultra-compact plasmonic filter with a fully controlled rejection band

In this article, we propose a novel approach to develop an ultra-compact spoof surface plasmon polariton (SSPP) band-rejection filter by loading T-shaped grooves on the SSPP transmission line (TL). This scheme is based on the interaction between two types of grooves, i.e. rectangular grooves of the SSPP TL and T-shaped grooves. This form of interaction has never been addressed before in order to achieve a highly efficient SSPP band-rejection filter. The working principle of this band-rejection filter is clearly revealed via investigation of the dispersion behavior of the SSPP TL in the presence and absence of T-shaped groove loading. Meanwhile, we simulate an SSPP TL loaded with T-shaped grooves. As proof of concept, we fabricate the filter in the microwave regime and perform an experiment which characterizes its functionality. The simulated and experimental results confirm the excellent filtering phenomena exhibited by our structure. The isolation of the filter can be less than −15 dB at rejection frequencies with excellent transmission efficiency in both passbands, before and after the rejection band. Furthermore, simulated near-electric-field results are also presented to demonstrate the authenticity of the filter. When the question of generating a highly efficient SSPP band-rejection filter arises, the proposed method facilitates us with T-shaped grooves, which are declared as an excellent alternative to metamaterial particles in this regard. The proposed band-rejection filter based on SSPPs demonstrates an outstanding capability to take part in the progress and the advancement of integrated plasmonic structures and systems at microwave frequencies.

A novel beam-steering device based on spoof surface plasmon polaritons

In this paper, an ultra-compact T-shaped component is proposed in order to achieve a spoof surface plasmon polariton (SSPPs) dual-functional device with beam steering and multiple band-rejection filtering functions. The newly introduced T-shaped component provides an excellent multiple band-rejection filter response when combined with the SSPP transmission line (TL), and can be regarded as an excellent alternative to metamaterial particles to conceive multi-band rejection of spoof SPP waves. Multi-band rejection filters are designed by introducing different intervals among the symmetric T-shaped components. Furthermore, we designed a compact SSPP beam-steering device integrated with a multiple band-rejection filtering function. The multiple band-rejection integrated beam-steering device can also be realized by incorporating different intervals among the T-shaped components, as mentioned in the case of linear filters. Integration of the SSPP beam-steering device and band-rejection filter offers compact areas and controllable passband features, which broadens the application range of SSPPs. In conclusion, the proposed T-shaped component is an outstanding addition toward the advancement of highly efficient ultra-compact dual-functional plasmonic devices.

Passive realization of the fractional‐order capacitor based on fractional‐order inductor and its application

SummaryThis paper investigates a new implementation of a passive fractional‐order capacitor (FOC) based on a single‐component fractional‐order inductor (FOI). The significance of this approach lies in providing the fractional‐order passive circuit to synthesize an FOC, which avoids the approximation that only depends on the integer‐order transfer function and reflects truly the infinite‐dimensional nature of fractional‐order impedance characteristic. For this purpose, the realizable conditions of this passive FOC are obtained and the main ideas of the proposed method are described by examples. The sensitivity of the impedance magnitude and phase angle on required components parameters is also analyzed in order to facilitate the design of the FOC emulator. Furthermore, the bandwidth is extended by modular structures connected in series, and the proposed approach shows an improvement over some previous methods in terms of accuracy. Also, based on the fractional calculus Grünwald–Letnikov definition, a single‐component FOI circuit element is packaged to build simulation circuit in Matlab/Simulink, and the effectiveness of the proposed method are validated by simulated and experimental results. In the application of an FOC, the results from in the series–parallel fractional‐order RLCβ bandreject filter circuit indicate that the fractional‐order counterpart can reduce the ripple and improve the suppression level at a certain frequency, and the peak amplitude and the overshoot decrease initially with decreasing order. Moreover, under the fixed inductance, capacitance, and resistance, the rise time varies almost inversely with order, whereas the setting time is on the decrease as the order is decreasing.

DV-EXCCCII Based Resistor-Less Current-Mode Universal Biquadratic Filter

This study aims to present a new resistor-less current-mode multi-input single-output universal filter. The current-mode’s design approach is used to obtain the proposed circuit. This circuit employs a single differential voltage extra-X current controlled current conveyor (DV-EXCCCII) and two grounded capacitors. This multifunction filter circuit offers low-pass, high-pass, all-pass, band-pass, and band-reject filters at a single output terminal without passive component matching constraints. The same circuit topology can obtain all second-order filter functions with different input conditions. The proposed circuit design is electronically adjustable with the bias current of DV-EXCCCII. Because of its high output impedance, this arrangement is suitable for cascading other current-mode circuits. The proposed circuit is simulated by Cadence Spectre with 0.18 µm UMC CMOS technology process parameters at ± 0.9 V supply voltages. The simulation results agree well with the theoretical concept of the proposed circuit.

An innovative fractal monopole MIMO antenna for modern 5G applications

Proposed in this paper is the design of an innovative and compact antenna array which based on four radiating elements for multi-input multi-output (MIMO) antenna applications used in 5G communication systems. The radiating elements are fractal curves excited using an open-circuited feedline through a coplanar waveguide (CPW). The feedline is electromagnetically coupled to the inside edge of the radiating element. The array’s impedance bandwidth is enhanced by inserting a ground structure composed of low–high-low impedance between the radiating elements. The low-impedance section of the ground is a staircase structure that is inclined at an angle to follow the input feedline. This inter-radiating element essentially suppresses near-field radiation between adjacent radiators. A band reject filter based on a composite right/left hand (CRLH) structure is mounted at the back side of the antenna array to reduce mutual coupling between the antenna elements by choking surface wave propagations that can otherwise degrade the radiation performance of the array antenna. The CRLH structure is based on the Hilbert fractal geometry, and it was designed to act like a stop band filter over the desired frequency bands. The proposed antenna array was fabricated and tested. It covers the frequency bands in the range from 2 to 3 GHz, 3.4–3.9 GHz, and 4.4–5.2 GHz. The array has a maximum gain of 6. 2dBi at 3.8 GHz and coupling isolation better than −20 dB. The envelope correlation coefficient of the antenna array is within the acceptable limit. There is good agreement between the simulated and measured results.

Common-Mode Driven Synchronous Filtering of the Powerline Interference in ECG

Powerline interference (PLI) is a major disturbing factor in ground-free biopotential acquisition systems. PLI produces both common-mode and differential input voltages. The first is suppressed by a high common-mode rejection ratio of bioamplifiers. However, the differential PLI component evoked by the imbalance of electrode impedances is amplified together with the diagnostic differential biosignal. Therefore, PLI filtering is always demanded and commonly managed by analog or digital band-rejection filters. In electrocardiography (ECG), PLI filters are not ideal, inducing QRS and ST distortions as a transient reaction to steep slopes, or PLI remains when its amplitude varies and PLI frequency deviates from the notch. This study aims to minimize the filter errors in wide deviation ranges of PLI amplitudes and frequencies, introducing a novel biopotential readout circuit with a software PLI demodulator–remodulator concept for synchronous processing of both differential-mode and common-mode signals. A closed-loop digital synchronous filtering (SF) algorithm is designed to subtract a PLI estimation from the differential-mode input in real time. The PLI estimation branch connected to the SF output includes four stages: (i) prefilter and QRS limiter; (ii) quadrature demodulator of the output PLI using a common-mode driven reference; (iii) two servo loops for low-pass filtering and the integration of in-phase and quadrature errors; (iv) quadrature remodulator for synthesis of the estimated PLI using the common-mode signal as a carrier frequency. A simulation study of artificially generated PLI sinusoids with frequency deviations (48–52 Hz, slew rate 0.01–0.1 Hz/s) and amplitude deviations (root mean square (r.m.s.) 50–1000 μV, slew rate 10–200 μV/s) is conducted for the optimization of SF servo loop settings with artificial signals from the CTS-ECG calibration database (10 s, 1 lead) as well as for the SF algorithm test with 40 low-noise recordings from the Physionet PTB Diagnostic ECG database (10 s, 12 leads) and CTS-ECG analytical database (10 s, 8 leads). The statistical study for the PLI frequencies (48–52 Hz, slew rate ≤ 0.1 Hz/s) and amplitudes (≤1000 μV r.m.s., slew rate ≤ 40 μV/s) show that maximal SF errors do not exceed 15 μV for any record and any lead, which satisfies the standard requirements for a peak ringing noise of < 25 μV. The signal-to-noise ratio improvement reaches 57–60 dB. SF is shown to be robust against phase shifts between differential- and common-mode PLI. Although validated for ECG signals, the presented SF algorithm is generalizable to different biopotential acquisition settings via surface electrodes (electroencephalogram, electromyogram, electrooculogram, etc.) and can benefit many diagnostic and therapeutic medical devices.